Angiogenesis, the growth of new blood vessels from preexisting vasculature, is a fundamental process in a variety of physiological and pathological conditions including wound healing, embryonic development, chronic inflammation, and tumor progression and metastasis (J. Folkman, Nat. Med. 1 (1995), pp. 27-31; W. Risau, Nature 386 (1997), pp. 671-674). In the course of angiogenesis, complex cellular processes take place, including degradation of extracellular matrix, proliferation, migration, and morphological differentiation of endothelial cells to form tubes. This entire process is orchestrated by local factors that modulate neovascularization (F. Bussolino, et al., Trends Biochem. Sci. 22 (1997), pp. 251-256), and changes in the angiogenic balance can mediate the ‘angiogenic switch’. Perturbation of the angiogenic switch can cause severe problems in the blood vessels.
Calcium plays a key role in signaling events evoked by various extracellular stimuli and coordinating a large variety of cellular functions (M. J. Berridge, Nature 361 (1993), pp. 315-325; K. Kiselyov, et al., Cell Signal 15 (2003), pp. 243-253). Increased intracellular Ca2+ is indispensable for adhesion, collagenolytic activity, migration, and proliferation of human endothelial cells and capillary outgrowth in vivo (E. C. Kohn, et al., Proc. Natl. Acad. Sci. USA 92 (1995), pp. 1307-131). Actually, vascular endothelium growth factor (VEGF), a receptor tyrosine kinase (RTK) ligand, and sphingosine-1-phosphate (S1P), a G-protein-coupled receptor (GPCR) ligand, induce neovascularization by modulating intracellular Ca2+ levels (M. Faehling, et al., FASEB J. 16 (2002), pp. 1805-1807; M. Guidoboni, et al., Cancer Res. 65 (2005), pp. 587-595). Therefore, investigating the Ca2+-mobilizing properties in endothelial cells might provide important information for the comprehensive understanding of the physiological processes involved in angiogenesis.
The strategy of positional-scanning of synthetic-peptide combinatorial library (PS-SPCL) has been used to isolate peptides that have angiogenic potential (R. A. Houghten, et al., Nature 354 (1991), pp. 84-86). Moreover, the PS-SPCL method has successfully been applied to screen useful peptides that are involved in various biological processes, resulting in the identification of several peptides such as interleukin-8-specific antagonists (S. Hayashi, et al., J Immunol. 154 (1995), pp. 814-824), inhibitor for nuclear factor of activated T cells (J. Aramburu, et al, Science 285 (1999), pp. 2129-2133), and the immunomodulatory peptides (Y. S. Bae, et al., Blood 97 (2001), pp. 2854-2862).